Feature : Support SPLADE pooling

### Feature request

I want to run the `https://huggingface.co/prithivida/Splade_PP_en_v1` using infinity. While it loads the model, but the output isn't the sparse representation. It being a sparse embedding model, the huggingface Text Embedding Interface documentation says we need to set the `pooling` to `splade`. I am not sure if that solves the issue and will output sparse representation but the idea is to support sparse representation output.

### Motivation

Embedding support for hybrid retrieval, infinity already support Dense models, supporting Sparse model would make it more versatile and drop in tool for hybrid retrieval approach

### Your contribution

Went through previous issues but found nothing relevant

Start by tracing Infinity's model-loading and embedding-output path for the Hugging Face SPLADE model, then compare it with the Hugging Face Text Embedding Interface guidance for `pooling=splade`. Done means Infinity can return the model's sparse representation while preserving existing dense-model support.

Written by the indexing model from the issue text.